Automated solar still

ABSTRACT

An automated solar still is disclosed which incorporates a system of valves and other controls that halts production when the level of solar insolation is not adequate to support evaporation, admits water for treatment only when the still requires resupply, operates at nominal pressure by gravity flow and flushes out suspended and dissolved contaminants automatically. Production is halted under conditions of inadequate solar insulation by means of a temperature sensitive valve which is exposed to the received sunlight. In one embodiment, heating and evaporation occur directly in a central chamber. In another embodiment heating occurs in external panels and evaporation occurs from trays in an evaporation chamber. With changes in dimensions and proportions the system of controls may be used in solar stills for desalinating sewater.

This application is a continuation-in-part of Robert L. Wyckoff,"Automated Solar Still", Ser. No. 528,399, filed Sept. 1, 1983, nowabandoned which was a divisional of Robert L. Wyckoff, "Automated SolarStill", Ser. No. 287,416, filed July 27, 1982 and now abandoned.

The present invention relates to solar distillation and in particulardiscloses a solar still encompassing a system of piping and varioustypes of valves so arranged as to make the still independent ofsupervision in its operation and easy to maintain. Capital investment isminimized by the simplicity of the design. Once installed it requiresonly sunshine and a source of feedwater at a pressure adequate to enterthe still. The piping circuit contains only three small ordinary floatvalves, one manually adjustable turn off valve and a temperaturesensitive valve. A special temperature sensitive valve in a deployedpanel is disclosed that is made of bent pipe and some wax but morecomplicated temperature sensitive valves could certainly be used.

BACKGROUND ART

The origins of solar distillation are lost in antiquity. The techniquehas not lent itself to general application because of the cumbersome,unattractive and generally manually operated equipment. People are nowaware that household water may carry chemical contamination and many arebuying electric stills which are expensive to operate and require muchoutside energy. Others rely upon filters which are usually onlypartially effective. Some persons carry expensive bottled water from thegrocery market while others pay for home delivery of water madeexpensive by the fuel and labor necessary to deliver it. The presentinvention discloses a method of solar distillation for the home. Theunit can be made attractive, compact, easy to operate and so simple tomaintain and install that most homeowners can service the stillthemselves. The size of the still can be readily altered to match theexpected incidence of sunlight for a given area and the required supplyof pure water.

DISCLOSURE OF THE INVENTION

The actual configuration of the solar still will vary with therequirements of output, amount and angle of sunlight and the need forspace. The specific embodiments set out in this specification are forrooftop installation designed to supply household needs for pure water.It is understood that certain spatial relationships may be changedwithout altering the concept of this invention. The arrangements of thevalves in sequence is a convenient order but the sequence could bealtered into any number of different sequences without violating theconcept herein disclosed.

A source of feedwater such as a well or a water main is connected to theentry pipe of the still. The entry pipe is first passed to the reservoirof distilled water in the bottom of the machine where a float valvepermits further passage into the machine when additional water isneeded. The feedwater then ascends within the entry pipe to thefeedwater reservoir open at the top of the still. Here, a float valvepermits the new feedwater to enter from the pipe only as it is needed tomaintain the proper operating level in this feedwater reservoir. Thisfeedwater reservoir extends over a portion of the top area of themachine, is shaded to prevent warming by the sun but open to the air topermit free evaporation for heat loss. In one embodiment, thedistillation chamber is an insulated chamber with one glass face throughwhich sunlight enters. A series of reflectors outside the evaporationchamber concentrate the light and heat of the sun into the distillationchamber. In the distillation chamber are a series of distillation traysone above the other and interconnected so that water entering the toptray would after reaching the operating level in that tray flow downinto the next serially until it reached the bottom tray. In anotherembodiment, a series of heat absorbing panels are deployed on the sidesof the machine. Feedwater flows from the reservoir through the topmostpanel and then into the topmost distillation tray. The water then flowsto the next panel, then to the second tray and so on. The water isheated in the panels and evaporates in the trays. In the firstembodiment, a condensation plate is provided on the underside of thefeedwater reservoir; in the second embodiment a condensation plate isprovided along the side of the feedwater reservoir.

Two valves are incorporated into the piping of the solar still. Thefirst valve is a temperature sensitive valve which consists of aquantity of wax which is sufficient size that when it is hardened it canocclude the entry pipe or top panel and which is situated at the top ofthe inverted U just below the entry level of the feed pipe or within thetop panel. The wax floats on the water filling the pipe and is trappedat the top of the inverted U. When the sun is shining and it is desiredthat the still should take on feedwater for distillation, the water canlace its way through the melted wax, but when the still cools and cannotprocess any more water the wax sets and occludes the pipe backing waterup in the feedwater reservoir where, as the water level rises, theintake float valve is actuated and stops further feedwater intake. Thepressure in the pipe where the wax is trapped is very small. The slowflow at low pressure within the pipe permits ample time for globules ofmelted wax carried by the water to float back into position before theycan be carried through the piping and out of the still. In applicationsthat bring greater pressure to bear on the wax a check valve at theentry end of the pipe would prevent emptying of the pipe and loss of thewax and a constriction at any point beyond the wax would slow the floatvalve in the bottom tray which serves to control the feedwater flow backinto the beginning of the working portion of the distillation still.Thus feedwater from the reservoir can enter the working portion of thestill only when the temperature is high enough for distillation to occurand when the distillation trays need recharging. From the bottomdistillation tray a pipe extends from the low point of the tray to theoutside. On this pipe is a manually controlled valve which can be set toallow any amount of fixed flow from the bottom tray in the distillationchamber. This flow is set at a rate of about one-fourth the expectedmaximum distillation rate and serves to carry out suspended anddissolved materials which were in the feedwater. The distilled waterreservoir in the base has screened vents to permit cooling.

An object of this invention is to provide a system to make solardistillation practical for the individual user by the use of aninexpensive and simple sequence of devices suitably arranged to permitreliable and automatic operation with a minimum of supervision andmaintainence.

A second object of this invention is to provide a simple, inexpensiveheat sensitive valve for use in solar devices and in other similarapplications.

Another object of this invention is to provide a solar distillationdevice which may be shipped or stored as a compact unit but which maydeploy a large field of solar collectors.

These and other objects of the present invention will become apparenthereinafter wherein the best mode for carrying out the invention isdisclosed with reference to the appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

For a more complete understanding of the solar distillation device ofthe present invention reference may be had to the accompanying drawingswhich are incorporated herein by reference and in which:

FIG. 1 is the left end view of a machine incorporating the system ofcontrols in accordance with this invention;

FIG. 2 is the front view of the machine of FIG. 1;

FIG. 3 is the right end view of the machine of FIG. 1;

FIG. 4 is a diagrammatic view of a system in accordance with the presentinvention;

FIG. 5 is perspective view of the machine of FIGS. 1-3 with a singlesolar reflector in place:

FIG. 6 is a drawing of the temperature sensitive valve with waterforcing its way through the melted wax;

FIG. 7 is a partial view of the temperature sensitive valve of FIG. 6wherein the wax is hardened thereby closing the pipe to the passage ofwater;

FIG. 8 is another partial view of the temperature sensitive valve ofFIG. 6 showing heat conducting vanes attached to the operative portionof the valve to increase its sensitivity to temperature change and toshorten its response time;

FIG. 9 is a front view of another solar still embodiment in accordancewith the present invention with sunlight-receiving panels in deployedposition;

FIG. 10 is a plan view of an individual sunlight-receiving panel fromFIG. 9;

FIG. 11 is a side view of the sunlight-receiving panel;

FIG. 12 is a side view of portion of a sunlight-receiving panel which iscrimped to form a variation of the temperature sensitive valve of FIGS.6-8;

FIG. 13 is a diagrammatic view of the solar still of FIG. 9;

FIGS. 14a and 14b are side cross sectional views, of a float valve whichshow, respectively, the closed and open positions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

By reference to the Figures it can be seen that a first embodiment ofthe present invention is portrayed in FIGS. 1-5, a second embodiment inFIGS. 9-13, and various valves are shown in FIGS. 6-8 and 14a-b. Thefirst embodiment is ideally encased in a single unitary cabinet but canbe funtionally separated into three portions. The first is the distilledwater reservoir 2 in the base which is vented to the air by screenedvents 24 which permit evaporation and cooling of the stored water whileprotecting it from contamination by rodents, birds or insects. Thescreened vents can be removed for cleaning and one end of the cabinetcan be removed for maintainence or major cleaning. The stored distilledwater is drawn down into the house as it is needed through outlet pipe20 drawing from above the bottom level of the tank to avoid drawing offany settled dust or sediment. The second functional portion of themachine is the top portion which is the storage tank for feedwater 6awaiting further progress into the machine. This storage tank also is ameans of breaking the pressure of the intake source and of fixing thepressure upon the remainder of the system. This feedwater reservoir 6has a metal bottom 7 which acts as the condensation plate of the still.The condensation plate 7 is slanted so that water runs down to the endwhere it drips off into a drip pan 18 which delivers it to the distilledwater reservoir 2 in the base through pipe 19. The feedwater storagetank 6 is open to the air to permit evaporation and cooling but shadedby a cover 23 to reduce warming by the sun. The third and largestportion of the machine is the evaporation chamber which in the presentform as pictured is above the distilled water reservoir and below thefeedwater reservoir-condenser 6, 7. The evaporation chamber is aninsulated chamber with a glass face 21 tilted so as to capture as muchas possible of the light and heat of the sun. The glass face 21 isringed by a series of reflectors 22. For simplicity of illustration thereflectors 22 are omitted from all drawings except for the singlereflector shown in FIG. 5. Connecting these disparate parts forfunctional purposes are pipes and valves which will now be described indetail with reference to the drawings.

For a household application in accordance with the first embodiment ofthe present invention, shown in FIGS. 1-4, feedwater from a water mainor well, lacking in purity, is directed into the intake pipe 1 whichleads to a float valve 3 which is controlled by the level of distilledwater in the distilled water reservoir 2. If more distilled water isneeded to replenish the distilled water reservoir 2 the feedwaterproceeds under pressure from its source to a second float valve 4controlled by the level of feedwater in the feedwater reservoir 6. Whenthe feedwater reservoir needs replenishment to maintain its level thefloat valve 4 permits feedwater to enter from the end 5 of the pipe 1.The pressure of the feedwater source is now broken and pressure in theremaining pipes of the input system is limited by the height of thefeedwater reservoir 6 over the level of the level of the outlet 29 ofthe input pipe 8. To prevent a buildup of salts and sediments in thesolar still a certain amount of the water must pass through to carry outsolid and disolved matter. For this purpose a pipe 16 extends downwardlyfrom the low point of the bottom evaporator pan 12 and carrieswastewater out of the machine at a rate controlled by adjustable valve17. The valve on the outflow is set so that about one fourth of inflowat optimal operating conditions passes out of the still as wastewater.The evaporating pans within the evaporating chamber are interconnectedso that the input water which feeds into the top pan 10 fills it firstand then progresses through pipe 14 to the next pan 11; then when pan 11fills to its operating level input water empties into the bottom pan 12via interconnecting pipe 15. The pipe 8 which carries the feedwater fromits reservoir 6 to the top pan 10 where the evaporative process firstoccurs, follows a long convoluted course containing two valves. The pipe8 drops vertically from the feedwater reservoir 6 and after aconsiderable course makes a U turn proceeding upward again toward thetop of the evaporative chamber, but just before reaching that level itagain makes a U turn once more directing it downward. Filling the lumenof the pipe at inverted U section 9 is a quantity of wax with a meltingpoint which has been determined to the minimum effective operatingtemperature of the solar still as measured in the evaporating chamberfor a particular location or application. When the temperature is toolow for satisfactory operation the wax hardens and the feedwater isunable to pass into the evaporating pans causing it to back up until thefloat-valve 4 on the feedwater reservoir closes. When the evaporativechamber reaches operating temperature the wax melts permitting water tolace its way through the valve 9, as shown in FIG. 6 where the water isindicated as 9b and the wax as 9a. To make the valve more sensitive totemperature change, fins or vanes 27 fabricated of heat conductingmaterial may be placed around the pipe 8 at the location of inverted Usection 9. When utilized with a low pressure flow, as described, the waxthat may be carried down the pipe 8 a short distance rises back upagainst the current of the water due to the difference in specificgravity. If there is danger that the flow may be more rapid and wash outthe wax or if there is a danger that the water in the pipe may dry outpermitting the wax to flow out, a check-valve 28 may be installed at thebeginning of the pipe to prevent drying or emptying and constrictionssuch as a fine mesh screen may be placed anywhere along the pipe pastthe valve 9 and before the outlet end 29. The temperature sensitivevalve just described has most immediate application to solarinstallations of all types but the principle of this valve of workingupon melting point and specific gravity differences to two immisciblefluids (one of which is more easily transformed into the solid state)has broad general application. The U may be upright when mercury is thetemperature sensitive agent or if lead is used. In instances where thetemperature sensitive agent is more dense than water the flow will alsodepend upon the pressure head so the valve also functions as a pressuresensitive valve. The possible combinations are myriad. Once past thetemperature sensitive valve the feedwater flows down to the level of afloat valve 13 which floats in and is controlled by the level of thewater in the bottom evaporation pan 12. The level of water in the bottompan is subject both to evaporation and to the controlled outflow throughwastewater pipe 16; therefore, pan 12 first reflects the need for morefeedwater into the evaporative pans. When the level of water inevaporative pan 12 drops it permits the feedwater to pass on up the pipe8 to the top pan 10 where the water enters through the end 29 of thepipe 26 after passing through any constriction (not shown) that might beused to reduce the flow rate to prevent outflow of the wax 9a in the waxvalve 9. In addition, to prevent the passage of wax beyond wax valve 9the pipe 26 may be distorted or constricted.

An alternate embodiment of the solar distillation still of the presentinvention is shown in FIGS. 9-13. In this embodiment the unit is storedor transported in a non-functional condition, and is rendered functionalby deployment of heat absorbing panels, as shown in FIG. 9. Then samegeneral distillation principle applies to the alternate embodiment aspertains to the first as seen by reference to the diagrammatic view ofthe distillation process given in FIG. 13. In both embodiments the fluidflow into the distillation system is regulated by the water level in thelast evaporation tray. The flow is further regulated by a temperaturesensitive valve (9 in FIG. 4; 67 in FIGS. 13 and 12 ) which admits waterinto the system only when the temperature of the fluid is high enough toexperience appreciable evaporation. The distinction is that in the firstembodiment the water is heated directly in the evaporation trays bysolar insulation whereas in the second embodiment the water is heated inpanels deployed outside the evaporation chamber. In the secondembodiment, after being heated the water is passed through evaporationtrays where evaporation occurs. The fluid flow sequence for the secondembodiment may be understood by considering, together FIGS. 9 and 13.

In FIG. 9 a solar still in accordance with the alternate embodiment ofthe present invention is shown in the deployed position. An evaporationtray compartment 36 has a front cover 33 which may be opaque tosunlight. This is permissible since the surface area of cover 33 isrelatively small compared to the total effective surface area of panels53, 54 . . . 58. A transparent front cover or top cover may be providedfor evaporation tray compartment 36 if the incremental solar insulationis worth the cost of the glass or clear plastic components; such costlycomponents are not required in accordance with this invention. Incomingenergy is collected primarily in the deployed panels 53, 54 . . . 58 asthe water flows through heat conducting water tubes which are mounted inthermal contact with the panels or are formed integrally with them.

An illustrative panel 59 is shown in plan view in FIG. 10. A relativelythin sheet 64 of heat conducting material such as aluminum, copper ortreated plastic, is formed with a tab 52. Preferrably, sheet 64 willhave a blackened front surface and an insulated back surface (notshown). When panel 59 is deployed, the tab 52 is bent at right angles tothe body of the panel. The bent tab, shown in FIG. 11, is inserted intoa bracket (not shown) formed in a side 31 or 32 of evaporatorcompartment 36; alternately, tab 52 rides in a slot formed in side 31 or32. Water enters tube 60 through inlet end 62 at the level of the panelfrom an associated evaporator tray, as discussed with reference to FIG.13, flows through tube 60 around the periphery of panel 59 and isdischarged through tube extension 61 and into a side 31 or 32 ofevaporator tray compartment 36 and thence into the evaporator tray nextin sequence. Preferably, tube 60 is formed of a heat conducting metalsuch as aluminum or copper to readily receive heat from the heatconducting sheet 64 which comprises panel 59 and tube extension 61 ispreferrably formed of a pliable rubber or plastic to readily be attachedand detached from the sides 31 or 32 of evaporation tray compartment 36as the solar still is alternately deployed or removed from service. Toobtain the maximum size solar collection field for a given sizeevaporation chamber the tab of the topmost panel may be bent downwardlythereby allowing the upper half of the top panel to extend above the topof the cover of the evaporation chamber; in reverse fashion, the tab ofthe bottom panel may be bent upwardly thereby allowing the bottom halfof the lower panel to extend below the bottom of the evaporationchamber. The angle of presentment of the panels to solar insulation iscontrolled by the location of the aforementioned slots or brackets inthe sides 31 or 32 of evaporation tray compartment 36. In order topermit deployment at locations of differing latitude and longitude andto permit seasonal adjustment a multiplicity or brackets or slots willbe supplied on the sides 31 and 32. Thus the person operating the stillmay select the bracket or slot which provides the optimum angle forreceiving the greatest total amount of energy at a given time and place.In FIG. 9, the panels 53, 54 . . . 58 are of the same dimension asillustrative panel 59 shown in plan view in FIG. 10 and are deployed atan angle of 42° from the vertical with the surfaces 64 being orientedupwardly to receive sunlight throughout the day. The optimum packing forthe paddles on the sides 31 and 32 is obtained by placing the paddles atprogressively increasing depths from the front cover 33. In addition,the tabs may be bent and the panels deployed with respect to theevaporation chamber, as described previously.

The distillation process is seen in the diagrammatic view of FIG. 13.Here, feedwater from the water line 49 enters through float valve 50,such standard toilet float valves which are available from the AmericanStandard Company. When the surface 30 of stored feedwater 34 reaches asufficiently low level float 77 will have dropped and drawn arm 51downwardly, thereby opening valve 50 to admit water from water line 49.Valve 50 closes as float 77 rises to a preset level. Thus, the opening48 to inlet pipe 63 is continuously provided with feedwater at nominalpressure. In alternate embodiments, feedwater storage tank 35 issupplied with seawater, polluted well water, or other contaminatedliquids from which it is desired to produce potable water. In accordancewith the present invention the flow of water through the evaporationchamber and panels is by the force of gravity and is not otherwisepressurized.

A supply of water to be distilled is thus continuously available ininlet pipe 63 at a pressure determined only by the height of water level30. The water passes through valve 76 which is controlled by the waterlevel in the bottom evaporation tray 43. Additional water is admittedthrough valve 76 only when the water level in tray 43 subsides below apreset reference level. Valve 76 only prevents the trays in evaporationcompartment 36 from becoming overfilled or from being underutilized; itis not an on-off valve dependent upon external conditions. Water wouldcontinue to flow through valve 76 even if no evaporation were occuringsince there is normally a continuous discharge through outlet pipe 45and valve 47 which cleans out the still. A preferred version of valve 76is shown and discussed with reference to FIGS. 14a and 14b.

As water to be distilled passes through valve 76 it rises up to a leveladjacent to the inlet end 62 of the topmost panel 53, providing level 30in the feedwater tank 35 is maintained above the height of panel 53. Itconnects through the side 31 to the associated inlet end 62 so thatwater flows through the tube 60 in panel 53. Then, after being heated anincremental amount, the flowing water is discharged through theassociated tube extension 61 and into inlet tube 38' which delivers thewater into topmost evaporation tray 38. In tray 38 evaporation occurscontinuously. Also, there is a continuous discharge of water throughoutlet 38" from tray 38 into the inlet end 62 of panel 54. The flowingwater is then incrementally heated and returned via inlet tube 39' intoevaporation tray 39 where additional evaporation occurs. This flowsequence is repeated for each of the trays in succession so that thewater flows from tray 39 to panel 55, from panel 55 to tray 40, fromtray 40 to panel 56 and so on until the water flows from panel 58 intobottom evaporation tray 43. In each tray evaporation occurs from thesurface, even though the water is continuously progressing downwardlyfrom tray to tray. The cumulative evaporation from tray 38 to tray 39and so on to bottom tray 43 is the source of potable water. Theevaporated water condenses on the side 37 of feedwater storage tank 35and drips into collection trough 46 from whence the distillate isdrained and is available as potable liquid. As with the first embodimentthe collection of sediment is avoided by maintaining a continuous,flushing flow of water through bottom evaporation tray 43 by means ofoutlet pipe 45 and conventional valve 47.

The penultimate regulation of flow in the automated solar still of FIGS.9-13, as with the embodiment of FIGS. 1-5, is provided by a temperaturesensitive valve. A separate valve such as valve 9, as describedpreviously, may be incorporated in the internal piping network. In apreferred embodiment, the temperature sensitive valve is incorporated inone of the panels. The panels are directly exposed to the incomingsunlight so they provide the best place to gauge the the temperature towhich the water is being heated. Preferably, this temperature sensitivevalve is included in the topmost panels because it is less likely to beshaded by the distillation chamber in the early morning or in the lateafternoon. In one embodiment the valve consists of a crimp along oneedge of a panel which necessarily elevates one portion 60' of tube 60above the remainder of the tube, as shown in FIG. 12. Within thiselevated portion 60' a quantity of wax is contained which is sufficientwhen hardened to occlude the tube 60. As discussed previously, when thesun is shining the water can lace its way through the melted wax.Preferably, a flexible tube connector 65 connects the separated ends ofsections of tube 60 so that melted wax may be injected by a hypodermictype syringe 78 if replenishment is required. In one embodiment thearcing portions 60' of tube 60 are fabricated from a transparent mediumso that the functioning of the valve may be monitored; in thisembodiment a colored wax 79 may be used to allow the ready visualobservation of the occlusion of the tube 60.

A possible float valve for use as valve 13 in FIG. 4 or as valve 76 inFIG. 13 is shown in FIGS. 14a and 14b. The float valve 76 could bemounted by a simple bracket (not shown) to the inside of the bottomtrays 12 or 43. Float valve 76 comprises a valve casing 70 within whicha valve stem 71 rides with vertical freedom. A bouyant float 68 isaffixed to the upper end of valve stem 71. Bouyant float 68 rides on thesurface 75 of the water 69 contained in the bottom evaporation tray 43.When the level 75 has reached its full height the valve stem 71 israised to the point where the flow through input pipe 63 is completelyblocked, as shown particularly in FIG. 14a. As the level of water intray 43 subsides, float 68 drops and valve stem 71 is lowered withincasing 70, thereby exposing narrowed neck section 72 of valve stem 71 tothe water in inlet pipe 63. Consequently, water flows around valve stem71 and into the tube 60 in panel 53 and eventually tray 43 refills asthe water wends its way from tray to panel, panel to tray and thence tothe bottom tray. When tray 43 refills the water level 75 rises and theflow of water through valve 50 is cut off as valve stem 71 rises to theposition of FIG. 14a.

A comparison of the direct heating embodiment of FIGS. 1-5 with theexternal heating embodiment of FIGS. 9-13 shows that the externalheating embodiment has a smaller evaporating chamber for a given solarcollection field. Thus, when stored or transported much less volume isrequired. In addition, no expensive and fragile glass or plasticmaterials are required; metal or wood components may be usedexclusively. In general, the limiting criterion is that there besufficient cumulative area in the evaporating trays to meet theestimated water requirements. Since the evaporating trays of theexternal heating embodiment do not need to share the solid angle ofsolar insulation they can be densely stacked as seen in FIG. 13 and asignificant evaporation area can be housed in a small volume. Inaddition, the external heating embodiment is preferred because of easeof packing and shipping as the panels can be stacked, less material isrequired and mass production is more readily accomplished.

I claim:
 1. An automated solar still having a temperature sensitivevalve incorporated within a deployed solar absorber panel, comprising:afeedwater storage tank having an opening for supplying feedwater atnominal pressure; an evaporation chamber containing a series ofevaporation trays for receiving and evaporating said feedwater and acondensor plate for condensing water vapor, said series of evaporationtrays being affixed within said evaporation chamber in spaced apartrelationship at descending heights, the upper tray of said series oftrays being connected by a pipe to said opening of said feedwaterstorage tank, said upper tray of said series of trays being positionedbelow said opening of said feedwater storage tank so that feedwater mayflow by gravity through said pipe from said feedwater tank into saidupper tray; a series of solar absorber panels detachably attached to theexterior of said evaporation chamber, each of said solar absorber panelshaving a fluid-tight conduit for passage of said feedwater, each of saidsolar absorber panels being associated in one-to-one relationship with aparticular tray in said series of trays; a piping network for feedingfeedwater from a particular tray to the associated solar absorber paneland for feeding feedwater from said associated solar absorber panel tothe next lowest tray from said particular tray, said piping networkincluding a series of inlet pipes connected between particular trays insaid series of trays and the inlet of said fluid-tight conduit in saidassociated solar absorber panel, and further including a series ofoutlet pipes connected between the outlet of said fluid-tight conduit insaid associated solar absorber panel and said next lowest tray; and atemperature sensitive valve incorporated within said fluid-tight conduitin one of said panels in said series of solar absorber panels, saidvalve thereby being in thermal communication with said feedwater flowingthrough said fluid-tight conduit in said one of said panels, wherebysaid valve is open when the temperature of said feedwater is at or abovethe threshold temperature for evaporation within said series of trays insaid evaporation chamber and wherein said valve is closed when thetemperature of said feedwater is below the threshold temperature forevaporation within said series of trays in said evaporation chamber. 2.An automated solar still in accordance with claim 1 wherein saidtemperature sensitive valve is incorporated in said panel associatedwith said upper tray.
 3. An automated solar still in accordance withclaim 1 wherein said temperature sensitive valve comprises a crimpedsection of said one of said solar absorber panels wherein saidfluid-tight conduit is crimped into an inverted U-shaped, said invertedU-shaped portion of said conduit containing a material immiscible inwater, the melting point of said immiscible material being near theminimum effective operational temperature of said solar still.
 4. Anautomated solar still in accordance with claim 3 wherein said invertedU-shaped portion of said conduit is transparent and wherein saidimmiscible material has a color to be readily visible through saidtransparent inverted U-shaped portion of said conduit.
 5. An automatedsolar still in accordance with claim 3 wherein said inverted U-shapedportion is separted in spaced apart relationship near its center andwherein the ends of said separated portions are connected by a flexiblemember to permit the resplenishment of said immiscible material byhypodermic apparatus.